This invention pertains to silicon-on-insulator (SOI) technology and, more particularly, to SOI substrates having relatively thick device layers with moderate thickness variation.
An SOI bonded wafer has a handle wafer, a device layer, and an oxide film (layer), constituting an insulating film, between the handle wafer and device layer. It is made from two semiconductor silicon wafers each having at least one face with a specular gloss finish. An oxide layer is formed on the specular glossy face of one or both wafers, and the two wafers are joined together with the specular glossy faces facing each other and with the oxide layer being between the two wafers. One of the wafers constitutes a handle wafer and the other constitutes a device wafer. The exposed surface of the device wafer is ground and/or etched and polished until the device wafer becomes a thin layer, i.e., the device layer. The joined wafers are heated to an appropriate temperature to increase the bonding strength.
Although various approaches have been proposed for fabricating SOI substrates, each has been found lacking in some respect. In general, certain of the methods proposed to date will produce SOI wafers with defect-free device layers having relatively low thickness variation, but these methods typically produce SOI wafers in relatively low yield and at relatively high cost. Other methods which have been proposed to date will produce SOI wafers in relatively high yield and at a favorable cost, but these methods typically produce SOI wafers having device layers which have an unacceptable thickness variation or which contain defects.